1. Field of Invention
This invention relates to an aerodynamic means that mitigate wind generated vortices and uplift loads on the roof perimeter area of a building, in a simple, effective, and economical way, applicable for both new constructions and retrofits of existing buildings.
2. Discussion of Prior Art
The previous and present roof construction practices normally lead to a roof perimeter configuration that tends to generate corner-edge vortex and subjects the roof perimeter area to severe uplift and high risk of wind damage. Structural methods have been used to mitigate the risk of wind damage. For example, builders may use stronger fasteners or smaller spacing between fasteners for roof cover and deck in the roof edge and corner area, and use “hurricane straps” in lieu of toenails to tie down the roof framing to the wall structure. Some aerodynamic methods have been recommended. Banks et. al. described in U.S. Pat. No. 6,601,348 (2003) various types of wind spoilers raised above the roof plane that function to mitigate edge vortex formation. However, the apparatus is rather complicated in shape and structure, and is susceptible to wind damage itself because the raised structure subjects itself to accelerated airflow across the roof edge. In U.S. Pat. No. 4,005,557 (1977), Kramer et. al. described conceptual designs for a roof wind spoiler system used strictly near roof corners. The limited breadth of the apparatus impedes its effectiveness and causes higher wind loads along the neighboring segments of roof perimeter, which the apparatus does not extend to. Its design is also only suitable for flat roofs. Ponder disclosed in U.S. Pat. No. 5,918,423 (1999) a wind spoiler ridge cap that is designed for protecting roof ridges, while this present invention deals primarily with roof perimeters. The structure disclosed herein is continuous along a roof edge or at least substantially extends from the roof corners towards the middle part of a roof edge. The designs are suitable for both sloped and flat roofs. The examples given hereafter are particularly suitable for roofs that have roof cover extending outwardly beyond the roof deck boundary and subjecting itself to accelerated upward flow deflected by the wall directly below.
In U.S. Pat. No. 6,606,828 of this applicant et al., a series of roof edge configurations are recommended for use to mitigate vortex and high uplift in flat-roof perimeter areas, where the concept is one of coordinated exterior curvature design for a roof edge system. The present invention discloses a distinct roof edge apparatus that utilizes overhung plates that preferably have face perforation and/or outer edge serration.